In the nuclear industry it is very desirable to have transfer systems that do not have any moving parts, i.e., pumps, valves, check valves, etc. The radiation fields and chemistry of the solutions quickly destroy any plastics, seals, and moving parts. Technologies that meet this criteria are jets, air lifts and fluidics. Fluidics is the technology dealing with the use of a flowing liquid or gas in various devices for controls, and fluid transfers.
In this industry it is also very desirable to produce unbiased samples and to transfer solution without dilution or concentration. Typically, air lifts and/or jet ejectors are used for sampling and solution transfers. A third option is fluidic pumping of the solution. Unlike gas jets, steam jets, or gas lift transfers, the fluidic transfer has the advantage that it does not concentrate or dilute the solution being transferred. Other fluidic transfer and fluidic sampling advantages are: (a) very high lift capability, (b) low sample scatter, (c) lower off-gas production with the attendant reduction in high-efficiency particulate HEPA filter consumption and environmental emissions, (d) dependability, and (e) very low maintenance.
Although, existing fluidic technology transfers fluids in one direction at approximately the same rate as air lifts and jets, the use of a vortex diode or reverse flow diverter (RFD) and jet ejector combination in bidirectional flow systems produces significantly higher transfer rates, i.e., 1.5 times faster than the base jet fluidic transfer rate and retains the fluidic system advantages.
Referring to FIG. 1, the basic prior art fluidic transfer systems use gas pressure 8 to transfer solution out of a pumping chamber 10, forcing the solution from the pumping chamber 10 into the feed tank, and the rest into a receiving tank 12 by operation of valves 14 (FIG. 1). The pumping chamber 10 is refilled with solution from the atmospheric-pressure feed tank 16 by gravity and the line to the receiving tank 12 as the air in the pumping chamber is vented to the feed tank through an orifice 18 in vent line 19.
A major improvement on the fluidic transfer system is accomplished by the installation of a vortex diode or reverse flow diverter 20 (RFD) in the outlet line of the feed tank 16 as in FIG. 2. An RFD consists of a tangential entry into a cylinder with the exit port 22 located in the center of the cylinder. RFDs are designed to have a higher resistance to flow in one direction (spiral entry) than in the opposite direction (elbow-like flow path). This means the pressure drop flowing through a RFD at the same flow rate in one direction, is much less than the pressure drop of the fluid flowing through the RFD in the opposite direction. With the RFD, most of the solution is pumped to the receiving tank 12, the rest goes to the feed tank 16. The refill resistance of a RFD is essentially equivalent to a tee of the same inlet and outlet diameter. As the RFD has a low refill resistance, the pumping chamber 10 refills almost as fast as the basic system, hence the overall pumping rate is greatly increased.
Another transfer system improvement is accomplished by the use of a jet as in FIG. 3. The solution from the pumping chamber 10 passes through a jet ejector 24, entraining the solution from the feed tank 16, then transferring the combined solution streams to the receiver tank 12. Since the air is not used to pump solution from the feed tank 16 by the air passing through the jet 24, this fluidic system essentially uses the solution to be transferred to pump itself. This combination (FIG. 3) refills very slowly but pumps much faster, therefore the overall pumping rate for the jet system is better than the RFD (FIG. 2) only. The fluidic jet transfer also has a much greater lift capability than air lifts or RFDS. other combinations of RFDs and jets have produced small increases in the overall pumping rate. The major limiting factor on the pumping rate of these jet fluidic systems is the refill rate of the pumping chamber 10. The pumping jet is essentially the entire resistance in this reverse flow path and reduction in the refill time can be accomplished by reducing the refill resistance of the pumping jet.